A combustion gas-driven nailing machine is known which is adapted to strike a nail into a steel plate or a concrete by a driver connected to a piston, by injecting a combustible gas into a closed combustion chamber and forming a mixed gas of the combustible gas and air in the combustion chamber, igniting the mixed gas and burning the same, imparting a high-pressure combustion gas thus generated in the combustion chamber to the piston slidably held in a cylinder and thereby driving the piston with an impact in the cylinder, and striking the driver. A compressed air driven nailing machine is also known in which compressed air is introduced into a cylinder holding a piston, a piston is driven in the cylinder, a nail is thereby struck by a driver connected to the piston.
In the power driven nailing machine driven by the combustion gas and compressed air, a nose with a discharge port for striking out a nail therefrom toward a work and guiding the same is attached to a lower portion of a housing holding the cylinder. A driver connected to the piston is held and guided in the discharge port. A magazine holding a plurality of nails therein is connected to a rear portion of the nose. A nail supplied from the magazine to the discharge port of the nose is struck by the driver into the work disposed at a free end of the nose. In the combustion gas-driven nailing machine, a container filled with a combustible gas and a battery for igniting the combustible gas are both fixed in the machine, so that the machine is formed as a portable tool. Thus, it is possible to strike a nail into a work without being restricted by a power supply source, such as an electric power supply source and a compressed air supply source.
In the power driven nailing machine driven by a combustion gas, an outer circumferential wall of the nose in which the discharge port is formed is provided with a contact member slidably supported along the discharge port. The contact member is connected at an upper end portion thereof to a movable sleeve for opening and closing an intermediate portion between the combustion chamber and an exhaust port via a contact arm. When the contact member is moved up, the combustion chamber is shut off from the exhaust port, and the movable sleeve is operated so as to seal the combustion chamber, and make preparations for enabling the combustible gas to be introduced into the combustion chamber. When the contact member and a trigger are operated with the discharge port of the machine pressed to the work, the machine is started. Therefore, the contact member constitutes a safety unit that acts so that the machine cannot be started unless the discharge port is pushed to the work so as to operate the contact member.
In such a power driven nailing machine, the contact member is provided on an outer circumferential surface of a nose, and a contact arm for connecting the contact member and movable sleeve is provided along the outer circumferential surface of the nose. Therefore, if the contact member and contact arm are made to contact the work and the like in such a case when the machine is carried, or if the machine is made to drop by mistake, the contact member and contact arm is deformed or broken in some cases. In addition, the contact member and contact arm may be inadvertently operated by the hand of an operator or by the work when the contact member and contact arm inadvertently engage therewith. Therefore, there is a possibility that an accident may occur.
In order to prevent the contact member and contact arm from engaging with the work as mentioned above, and, in order to protect the nose and contact member against a shock occurring when the machine drops and the machine interferes with the work, a nailing machine provided with a protective shield so as to enclose the nose has already been proposed (refer to JP-A-2000-000781). However, in the nailing machine of JP-A-2000-000781, the protective shield is formed so as to enclose the nose as a whole, so that the outer dimensions of the nose become large. This causes the nail driven portion of the work to become difficult to be seen, and a nail driving operation for a narrow portion of the work to become impossible. Therefore, the operation efficiency decreases. In addition, since the protective shield is formed so as to cover a front portion of the nose, it is necessary to remove the magazine attached to a rear side of the nose, in order to remove a nail, when the discharge port of the nose gets clogged with the nails. Therefore, the nail removing operation carried out when the discharge port gets clogged with nails takes much time.
Moreover, a machine having a discharge port formed cylindrically for driving and guiding the nail toward the work, supporting the discharge port slidably with respect to the nose so that a free end of the discharge port projects toward a free end of a nose, and connecting an upper end portion of this discharge port to a movable sleeve also has already been proposed (refer to JP-A-2001-162560). In the nailing machine of JP-A-2001-162560, the outer dimensions of the nose can be set small, and the visibility of the nail driven portion of a work is improved. However, since the discharge port as a whole is moved, an operation of a timing for supplying a nail from a magazine to the inside of the discharge port is complicated, so that the construction of parts also becomes complicated. Moreover, since a link member by which the movable sleeve and discharge port are connected together is formed on an outer surface of a housing and connected thereto at a front portion of the nose. Therefore, a work and the hand of the operator touch the outer surface of the link member to cause the nailing machine to be broken or erroneously operated.